The surface area is 104 km2. The length of the lake is about 13 km, the width is 11.5 km. The maximum depth, depending on the water level, is 6-10 m. The lake is flowing. It is fed by the Tuldun, Indola, and Zhipkesen rivers. Through the Khorginsky lakes, a small shallow tributary of the Khola, the Eravninsky lakes are connected to the Vitim River. In the southwestern part, it is connected by a small strait to Sosnovy Lake. The village of Garam is located on the shore of the lake. Perch, pike, crucian carp, roach, and roach are found here. Peled, bream, and silver bream are also present.

The lake is part of the Eravninsky – Khorginsky lake system, which is located in the Baikal buffer zone, since these lakes are connected not only with each other by channels and groundwater, but also with the basins of the Uda and Selenga rivers, and ultimately with Baikal. They are located on the site of vast ancient lakes of the Mesozoic era. Three large lakes of the Eravninskaya system: Sosnovoe Island, Bolshaya and Malaya Eravna, are closely connected to each other and are, as it were, one limnological whole.
A whole galaxy of small lakes, scattered around the main systems of Eravninsky lakes, are not connected to them and are completely isolated from any influence of the main mass of large lakes. These include, for example, lakes: Shchuchye, Gunda, etc.

The Bolshoi Eravninsky lakes are located along the central part of the Eravninsky district. These lakes are of great importance – firstly, they are a source of drinking water for the population, secondly, a habitat for commercial fish, and thirdly, they serve as a wonderful place for recreation.